Angle-Multiplexed Hologram Storage
Angle-multiplexed hologram storage techniques can be used to store multiple images in an area on a holographic film. Angle-multiplexed hologram techniques can also be used to store multiple images via diffractive structures located in a material or on the surface of the material. Disadvantages of angle-multiplexed hologram techniques include their complexity, and limitations such as the use of binary variables which limits their security, and the slow write speed which makes them unsuitable as a real-time storage device.
Diffractive Nanostructures
Diffractive nanostructures can be used to store data on the surface of materials by exploiting the particular optical effects they create. Data can be encoded and represented in a multi-state system where colors or wavelengths can be used as variables. Since a data storage approach based on diffractive nanostructures takes advantage of a multivariable system to represent the data, the approach results in stored data that is more difficult to decode and therefore is more secure than other techniques.
The high resolving power of nano-scale diffraction gratings enables the detection of distinct spectral signatures, such as colors or wavelengths, and provides inherent physical data compression. The use of diffractive nano-structures can allow large amounts of data to be stored and encrypted optically in a small surface area. The approach can provide methods for authentication as well as machine-readability of stored data.
An image comprising diffractive pixels can exhibit color changes of higher intensity than holograms. In this context, the term pixel refers to a nano-structure or equivalently a nano-optical bit. Using diffraction gratings at varying angles, angle-dependent optical effects can be achieved by changing the illumination angle. Multiple images can be stored on top of each other on the same area of the surface, and visualization of each image can be enabled by selecting the direction and angle of incident light. Where there are multiple images, only one of the stored images can be seen at a given incidence angle, i.e., when the incidence angle is normal to the grating corresponding to the selected image.
The pixels used to construct each image can be square, rectangular, circular, oval or another suitable shape. The perceived color from each pixel depends on the orientation and periodicity of the grating used in the pixels. The periodicity of the grating generally ranges from 20 nm to 200 μm. The size of the pixels also varies depending on the periodicity of the grating. By choosing the periodicity carefully, the color of a digital image can be mimicked once it is translated into a diffractive image at a particular angle of incident light.
Diffractive images with improved control over a wide range of viewing angles per color can be fabricated by using a suitable type of grating design. Brighter and more eye-catching diffractive images can be achieved by modifying the periodicity of each pixel. The diffractive images can be stored in multiple layers via techniques such as imprinting, casting and the like.